As a semiconductor device that includes, for example, a nitride semiconductor stacked structure for which a nitride semiconductor is used, a high electron mobility transistor (High Electron Mobility Transistor: HEMT; GaN HEMT) in which, for example, GaN is used for a channel layer (electron transit layer) is available.
As such a GaN HEMT as just described, for example, a HEMT in which, for example, AlGaN, InAlN, InAlGaN or the like is used for a barrier layer (electron supply layer) is available.
Also a HEMT is available in which a cap layer for which, for example, AlGaN, GaN or the like is used is provided on the outermost surface of a nitride semiconductor stacked structure.